1. Field of the Invention
The invention relates to methods for manufacturing optical fiber probes and, particularly, to a method for manufacturing an optical fiber probe used to detect Raman signal.
2. Description of Related Art
The surface Raman spectrum plays an important role in diverse fields including surface-behavior science and materials science. More particular, surface-enhanced Raman scattering (SERS), in which the Raman spectrum intensity is found to be greatly enhanced, is observed for a large number of molecules adsorbed on the surfaces of metals. The Raman spectrum intensity enhancement can be up to 14 orders of magnitude so that the SERS technique has the merit of great sensitivity. Many mechanisms have been proposed over the past twenty years to account for the enhancement of the Raman spectrum intensity. With the development of high-resolution confocal Raman microscopy, great achievement has been made in development of the SERS technique. In addition, it is believed that the possibility of obtaining the surface-enhanced Raman spectrum of a single molecule would constitute a breakthrough progress in this area. For example, using such an SERS technique, it may then be possible to detect, e.g., a single molecule adsorbed on the surface of a single nano-scale silver particle. The results therefrom could potentially show extraordinarily high Raman spectrum intensity (1014 or so) and obtain the Raman spectrum with higher quality. Thus, the SERS technique is thought to be an important research tool for molecular science. Due to the high sensitivity of the SERS technique, it is also considered that the SERS technique is promising in the respect that it might be extensively used to detect the trace molecules in a solution or gas.
Using an optical fiber to detect a Raman signal allows the SERS technique to be employed, in practice. Referring to FIG. 4, a conventional optical fiber probe system 30 includes an optical fiber probe 32 and a spectrum analysis device 36. The optical fiber probe 32 has a first end 322 and an opposite second end 324. A metal thin film or metal particles is/are coated on the surface of the first end 322. Molecules adsorbed on the metal thin film or on the metal particles will generate intense SERS by illumination from an outer laser 34. The optical signals of the SERS are transmitted from the first end 322 of the optical fiber 32 to the second end 324 of the optical fiber 32. Then, the optical signals are received by the spectrum analysis device 36 from the second end 324 and then are analyzed. In such case, it is realized that the optical fiber probe 32 mentioned above is easily inserted into a sample 38 to be measured, instead of putting the sample 38 on a specific platform of a detection device. That is, the detection efficiency can be improved, and the optical fiber probe system 30, as a whole, can be fairly compact.
Additionally, referring to FIG. 5, another conventional optical fiber probe system 40 includes a single optical fiber probe 42, through which an activating light emitted from a light source 44 and a Raman scattering light from a surface of a specimen 48 both can travel together. The activating light emitted from a light source 44 is reflected, in turn, by a half mirror 442 and a reflective mirror 444 and subsequently focused by a focusing lens 46. The focused light enters the single optical fiber probe 42 from a second end 424 thereof and is transmitted through the single optical fiber probe 42 and emitted from a first end 422, so as to irradiate a sample 48. Then, the Raman scattering light produced from the surface of the sample 48 enters the single optical fiber probe 42 from the first end 422 and transmits to the second end 424. A spectrum analysis device 52 detects the light returning from the surface of the sample 48 in the light path of passing through the focusing lens 46, reflective lens 444, and half mirror 442, sequentially. In such case, the optical fiber probe system 40 mentioned above is favored for miniaturization because the activating light and the Raman scattering light use the same light path.
As mentioned above, the first ends 322, 422 of the optical fiber probe 33, 42 serving as detectors are generally coated with metal particles or the thin film by evaporation, electroplating, or sputtering. These methods are necessarily performed in a vacuum chamber or in an electrolyte. In addition, a heat treatment for the optical fiber is required to increase the adhesion quality and the roughness of the metal particles or the thin film.
What is needed, therefore, is a method for manufacturing an optical fiber probe that is easier and that has no requirement for additional vacuum device and heat treatment process.